From the prior art a collection unit for synthetic threads is known, in which synthetic threads are collected at a constant speed during the winding of the package.
The collection unit is equipped with one or more package-carrier spindle(s), a feeler roller, or motor-driven roller, and a traversing unit cam which is provided with cross helical slots for driving a thread-guide slider.
It is well-known that the control of revolution speed of the spindle to secure a constant collection speed takes place by means of the feeler roller. This roller is kept in contact with the circumference of the packages during the winding of the thread and is preferably driven by means of a variable-frequency synchronous or asynchronous electrical motor.
The difference between the peripheral speed of the packages, (which tend to increase with increasing package diameters), and the peripheral speed of the feeler roller cause a rotation in the internal part of the feeler roller. The internal part is supported by bearings, so as to be capable of rotating. This rotation acts on a potentiometer. A signal of the potentiometer regulates the new necessary revolution speed for the package-carrier-spindle driving motor to regulate and keep constant the package collection speed.
With reference to the field of "precision winding", the problems are very important and concern imperfections of the made-up threads. These problems are directly related to the principle of distributing the thread on the package.
The collection units which are designed to produce packages of wound thread nearly always lead to the formation of deposits of turns which are concentrated in some points. These deposits lead to the problem of ribboning.
Ribboning appears as a winding defect. The thread, while wound in mutually overlapping turn layers, forms compact thread cord-like bands on the package.
Incidentally, in the following disclosure, this defect will be called "ribboning", or "taping", or "mirror effects", with these terms being used interchangeably. These ribboning defects appear during the winding when the ratio of the number of revolutions (during a unit of time) of the package to the number of to-and-fro (double) strokes (during the same time unit) of the traversing device (i.e., of the thread-guide slider) and is represented by an integer.
Under these conditions, after a double stroke is completed by the thread-guide, the starting point of the turns which comprise the new layer coincides with the starting point of the previous layer.
This causes overlapped, hardened thread layers which form the ribboning, and are in the form of maximum-density tapings. The formation of ribboning compromises the correct unwinding of the thread which will be later unwound. It can further compromise the uniformity of liquid passage during a process of dyeing the bobbins. This can result in layers which are not uniformly dyed, and therefore can result in changes in the thread dyeing level. In order to prevent these drawbacks, a divisional ratio should be selected, to give the turns a small, suitable and advantageous shift which is relative to the preceding turns.
For example, the revolution speed of the bobbin varies over time. The purpose of this speed variance is to keep constant the peripheral speed of the package as its diameter increases. In this way the number of complete strokes performed during the time unit by the thread-guide slider remains constant. In this example, the ratio of the number of revolutions "N" of the package during a certain time unit to the number of complete, to-and-fro, strokes "Z" of the thread-guide slider during the same time unit will vary from a maximum value at the beginning of bobbin winding, down to a minimum value when the bobbin is full. This is a continuous process. Therefore intermediate integer values, as well as exact fractional values (such as 1/2, 1/4, and so forth . . . ; as well as n.sub.1 /2, n.sub.1 /3, n.sub.1 /4 . . . , occur (incidentally, n.sub.1 can be any integer relative to the denominator).
This ratio is defined hereinafter as the "winding ratio" ("K" value) of the package under formation. For each of said integer values, or of said exact fraction values, the formation of ribboning, i.e., the superimposition of a plurality of thread windings giving rise to the mirror effect, will occur.
Therefore, when the value of the winding ratio K passes through a value in the range of an integer or of an exact fraction value, tapings will be formed in the bobbin. The extent of said tapings is directly proportional to the amount of time the bobbin is wound within this range of values. The tapings which result reach their highest extent when the mirror effect is of the 1st order, i.e., when two layers superimpose upon one another with each winding having a "K" winding ratio of an integer value.
In an analogous way, mirror effects of the 2nd, 3rd, 4th order, and so on, occur when the thread is wound on the same point respectively after 2, 3, 4 and so forth . . . Layers, i.e., with a "K" winding ratio having an exact fractional value.
Therefore, the intensity of the phenomenon decreases with an increasing order of mirror effect.
From the above, the need arises to stagger the winding turns. In this way the time that the "K" ratio exists may be as short as possible to reduce the above mentioned mirror effects in the winding of the thread collection package.
The above described method distributing the thread on the package represents a "random" winding.
Another method of distributing the thread on the package comprises keeping a ratio of the number of revolutions "N" of the package (during a certain time unit), to the number of complete, to-and-fro strokes "Z" (during the same time unit) during which the thread-guide slider remains constant. When the peripheral speed of the package remains constant with an increasing winding diameter (that is, the thread collection speed remains constant), a continuous and gradual decrease in the number of revolutions of the spindle results. A constant thread collection speed further results in the simultaneous reduction in the number of complete strokes of the thread-guide slider. It is known that the cam which drives the thread-guide slider is itself driven by a variable frequency motor by means of an inverter.
The method of distributing the thread on the package according to this method represents a "precision" winding.
By means of such a distribution, the value of the winding ratio "K" remains constant. The value which is selected for the winding ratio "K" at the beginning of package winding should be a fractional number which is capable of giving each turn a shift relative to the preceding turn. For example, if the shift is small and approximately corresponds to the diameter of the thread, a compact bobbin is obtained. If on the contrary, the shift is considerably larger than the diameter of the thread, a porous winding is obtained. A porous winding would be particularly suitable for a following dyeing process.
In light of the above, the thread collection should occur under conditions which would avoid the values which cause ribboning problems. Therefore thread should be wound with an uniform distribution of turns on the circumference of the package under formation. However, "precision winding" has considerable disadvantages which render it unsuitable for larger package diameters which are presently used. For example, as a result of the decrease in the reciprocating speed of the thread-guide, the collection speed decreases with an increasing package diameter. This causes negative effects on the constancy of the count of the wound thread. Furthermore, an excess difference occurs between the initial winding angle and the final winding angle of the last thread layer on the package.
The winding angle is the angle at which the thread winding meets perpendicular to the axis of the package. The stability of the thread package depends on this angle. In fact, an excessive initial winding angle causes a slipping of the thread layers. Too small of a winding angle at the end of winding causes the formation of side bulges due to poor mutual cohesion of the thread layers.
The compactness of the package also depends upon the winding angle. In fact, the more that the turns are cross-wound, the greater the winding angle, the lower the packing density of the threads, and the greater the softness of the package. The smaller the winding angle, the more compact the package. It is evident that during winding the thread on the package, the winding angle should remain constant, or, at most, undergo a small variation around the value that was selected as the optimum value of the package. An excessive variation of the winding angle causes changes in compactness within the interior of a package. A variation in the compactness of the package renders it difficult to be used during subsequent steps in the manufacturing process.
Several techniques have been proposed and are used in the prior art to improve the characteristics of a package under formation in a collection unit for the high-speed collection of synthetic threads.
For example, a device is used in collection units which use the random type of winding which staggers the thread-guide slider stokes (the traversing device strokes) by means of an electronic system. This system is installed on an inverter which changes the frequency of the motor means actuating the traversing device cam.
Therefore, by means of such a device, modulation is introduced into the frequency of revolution of the cam. A modulation is consequently introduced of the frequency of the strokes of the thread-guide slider. In such a way, the dwell time of winding under conditions of integer-number of exact-fraction (such as 1/2, 1/4, etc...) "K" winding ratios, which cause ribboning, is decreased.
As a result, the ribboning effects remain, but the length of time during which the winding remains under those critical winding conditions decrease. However reduced though, the problem of overlapping of the wound thread remains. The above-described device merely reduces the occurrences of the phenomenon of ribboning. Such a device, although widely used, suffers from a serious drawback. That is, the attenuation of the ribboning (the mirror effect) is not constant, because its effect varies with the varying size of the package under formation.
Another different device which is suggested by the prior art to prevent the wound thread from superimposing upon one another, is based on forming the package with a succession of precision windings. These precision windings have constant, fractional values of the "K" ratio. The line portions have all the same length, and follow one another according to a decreasing-"K" order. They are united by substantially vertical portions which are obtained by means of a rapid increase in the frequency of the revolution of the thread-guide slider cam. This device results in a considerable improvement in the quality and characteristics of a package under formation having cross-wound turns.
Despite this improvement, from time to time faults of layers or thread positions occur in the cross-wound package. In fact, this device, even if it improves the distribution of the elementary layers of threads wound on the package does not ensure that portions of precision winding along which the collection unit operates, are spaced apart from a line having an integer "K" value, or with an exact-fraction "K" value, by a long enough distance.
Logically, when such closeness occurs, the thread is wound with a higher compactness. This winding can result in a ribboning, however faint, which will cause difficulties during the unwinding step during subsequent processing. The package which will be formed will therefore have, even in the best case, winding layers of varying degrees of compactness. This will impede the passage of liquid during a subsequent dyeing step. This passage of the dye will not be uniform, and the layers will be dyed in a non-homogeneous way.
These and other devices which are proposed in the prior art to ensure proper distribution of thread on the package have all resulted in an often uncertain operation. In fact, they have all resulted in varying degrees of ribboning and a winding which is not always repeatably within the desired quality level.
A purpose of the present invention is to eliminate the above said drawbacks by providing an automatic process and an apparatus which yields a faultless result. The invention will be reliable in the reproducibility of the quality of the winding to yield a uniform thread distribution along both the width and depth of the package, when packages of any size are formed.
Another purpose of the present invention is to wind the packages so that they have homogeneous compactness, or homogeneous softness, in all points of the package under formation to thereby render it perfectly permeable for the dyeing liquids.
A further purpose of the present invention is to maintain the collection speed within a limited range of values so that synthetic threads are wound without undergoing overstresses which would be capable of deforming the long elastic chains of the polymers and to preserve their physical properties.
These and still further purposes are all achieved by means of the process according to the present invention. This invention makes possible the values of the winding parameters to be constantly entered so that the collection unit operates along descending line portions. Each line portion is the locus of points having constant, non-integer and non-exact-fractional value of the "K" winding ratio. These ratios make possible that the line portions are contained within a range which is bounded by a maximum limit value and a minimum limit value of the winding angle. The maximum limit value and the minimum limit value are symmetrical to the value which is regarded as the optimum value for the package under formation. The minimum and maximum values can be about 5% higher and 5% lower than the optimum value. These values allow the traversing device cam to be controlled to fix the dislocation of the descending line portions at a distance longer than, or, at least, equal to , a reference value from a line belonging to those lines having integer or exact-fraction "K" values. These represent the orders of ribboning of the "mirror effect" which are considered to be harmful to the quality of the winding. The reference value is fixed and preset at a value not greater than, half the distance between the two nearest adjacent lines which belong to those having integer or exact-fraction "K" values.